Cancer Biology. Epithelium from human breast has been grown in culture and maintained for several weeks. Response of "hormone dependent" epithelium to hormones in vitro varies from species to species. Electrical communication is shown to occur between basal cell cancer cells, similar to that between normal epidermal cells. Redifferentiation of undifferentiated basal cell cancer cells occurs in tissue culture. Carcinogenesis. A breast biopsy vacucylinder to obtain cores of human breast has been constructed and tested clinically. A staging system for mycosis fungoides lymphoma has been developed using clinical, histologic, lymphangiographic and immunologic criteria. Organ cultures of lesions of mycosis fungoides have been successfully grown; in such explants many characteristic lymphoid cells with vermiform nucleus predominate. Cancer Therapy. Precutaneous adminstration of mechlorethamine has been found to cause complete remissions of mycosis fungoides lymphoma. Means to immunologically desensitize patients allergic to the drug have been perfected. Means to induce states of specific immunologic tolerance to the prior, prior to first topical exposure, have been developed. Both the foregoing require I.V. administration of minute amounts of drug.